To produce recesses and protrusions on a decorative material that has been used in knock-down furniture, a building material, furniture or the like, there is such a method that provides a visual effect of a three-dimensional impression of recesses or protrusions by differentiating the level of the state of luster between portions to be seen as protruding or portions to be seen as recessed on the surface so as to take advantage of the visual illusion of human recognition, instead of forming real recesses and protrusions on the decorative material. This method causes a portion having higher luster to be seen as if protruding and a portion having lower luster to be seen as if recessed by the human eye, when in fact there is no are recesses and protrusions.
The above-mentioned method is implemented, for example, by forming a luster control layer, from a transparent or semi-transparent synthetic resin paint having a controlled state of luster, over the entire surface of a substrate whereon an appropriate design including a recess pattern is printed, then forming a transparent or semi-transparent layer of an ionizing radiation-curable resin having a different luster level on a portion of the surface of the luster control layer except for the portion where the recess pattern or protrusion pattern is formed. The luster control layer and the layer of an ionizing radiationcurable resin include silica particles added for the purpose of adjusting the luster level and/or improving scratch resistance.
This method enables the rendering of a three-dimensional impression of recesses and protrusions to any substrate simply by providing the luster control layer and the layer of an ionizing radiation-curable resin having different luster levels, without using any special chemical. In addition, since the layers having different luster levels can be formed by a common printing method such as gravure printing after forming the design pattern, no special facility is required so that the process can be carried out with high productivity and matching with the design pattern can be easily achieved. Also because the paint layer can be far thinner than the height difference between the recesses and protrusions to be represented, consumption of the resin can be decreased and higher flexibility is achieved so that a decorative material having an excellent property on bending processing can be easily provided. Also because the decorative material does not have significant surface irregularities, there is such an advantage that stains do not accumulate in recesses.
Due to the many advantages described above, the decorative material based on the above-mentioned method has been used in large quantities, but has not yet excelled in a method of actually forming a high quality of recesses and protrusions. The reason can be considered as follows. A mechanical embossing method, for example, is capable of representing the configuration of the recesses and protrusions such as vessels of natural wood accurately including the sectional configuration. With this method that uses two kinds of paints having different luster levels, in contrast, surface luster is provided in two levels and therefore recesses and protrusions that can be represented are also provided in two levels. As a result, there is a problem that this method is not capable of representing the configuration of recesses and protrusions having slopes where depth (height) changes continuously as in the case of vessels of natural wood.
Accordingly, such a decorative material has been proposed (see, for example, Japanese Patent No. 3,629,964) that represents the configuration of recesses and protrusions having slopes where depth (height) changes continuously as in the case of vessels of natural wood, by providing a luster control layer that represents the configuration of recesses and protrusions having slopes where a depth (height) changes continuously.
However, the decorative material disclosed in Japanese Patent No. 3,629,964 has such a problem as containing silica particles therein for the purpose of adjusting the luster level and/or improving scratch resistance makes it easier for an oily substance such as paraffin oil or butter to infiltrate into the decorative material. An oily substance that has infiltrated may be removed, if it remains near the surface, by sucking out or wiping out. However, a stain that has infiltrated down to the substrate is difficult to remove, so as to remain therein thus giving rise to the possibility of ply separation and impairing the appearance.